Ion acceleration pulsed neutron generator



March 1955 J. v. BRADDOCK ETAL 3,173,013v

ION ACCELERATION PULSED NEUTRON GENERATOR Filed Dec. 20, 1961 2 Sheets-Sheet 2 //V VE/V TUES- YZ/OMns GBULLE V.

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United States Patent 3,173,013 ION ACCELERATION PULSED NEUTRON GENERATOR Joseph V. Braddock, 218 W. River; Bernard J. Dunn, 302 Oliva Circle; Daniel F. McDonald, 205 Sunset; and Henry A. Miranda, Jr., 4131 Larchmont, all of El Paso, Tex., and Thomas G. Bullen, 715 North Ave, New Rochelle, N.Y.

Filed Dec. 20, 1961, Ser. No. 160,741 7 Claims. (Cl. 250-845) This invention relates to neutron generators and particularly to apparatus for producing pulses of neutrons of high energy for laboratory and irradiation purposes.

Sources of neutrons of high energy are useful for many purposes and are used as a research tool in studying various atomic phenomena and as a commercial device for irradiating various materials, e.g., plastics, foods, etc., to change the properties thereof,

It is well known that when a deuteron and a triton collide with sufficient energy, a nuclear reaction instantaneously occurs in which a neutron is ejected with an energy of approximately fourteen million electron volts. Also, it is known that if tWo deuterons collide with sufficient energy, a neutron is ejected with an energy of approximately two million electron volts. Equipment utilizing the first reaction for the purpose of providing a source of neutrons has previously been employed, and in such equipment an ion gun is employed to produce deuterons which are accelerated in a relatively high vacuum t0- ward a target containing tritons. If the so accelerated deuterons have sufficient energy, neutrons are ejected from the target. Such prior art equipment has not been satisfactory not only because a separate ion gun assembly is required, but also because of an insufficient supply of deuterons, instability and uncontrolled discharges through the air external to the discharge tube. In the apparatus of the present invention ions are generated at a rate at least one hundred times greater than with ion sources of the prior art equipment.

In the preferred embodiment of the invention, a denterium or tritium gas is introduced into one portion of a continuously, but not highly, evacuated tube and such molecules are subjected to a high voltage field between a pair of spaced, electrically energized electrodes within the tube which causes ions of the gas to be generated and accelerated from adjacent one of the electrodes to: ward the other electrode which has a target surface containing the nuclei required for the production of neutrons. 'For example, if the gas introduced is a deuterium gas, then the target surface contains tritons for the production of high energy neutrons or contains deuterons for the production of lower energy (2 m.e.v.) neutrons. Alternatively, the gas may be a tritium gas, and the target surface will contain deuterons resulting in high energy neutrons.

The methods of the invention may be employed with various types of prior art apparatus with less satisfactory results, and we have also invented a preferred form of apparatus which has been found to give highly satisfactory results. Thus, with the apparatus of the invention, we have been able to produce consistently 4x10 neutrons, each of an energy of approximately fourteen million electron volts, in the form of a pulse of such neutrons, the duration of the pulse being approximately ten 3 ,1 73,0 1 3 Patented Mar. 9, 1965 "ice microseconds, such yield being several hundred times greater than that obtained with prior art devices. In addition, we have been able to obtain peak yields at least one thousand times greater than with prior art apparatus.

One object of the invention is to provide a method for producing a large number of high energy neutrons using relatively simple apparatus.

Another object of the invention is to provide a method and apparatus which will produce copious and sustained number of ions.

A further object of the invention is to provide improved and stable apparatus for generating a large number of high energy neutrons.

Other objects of the invention will be apparent from the following detailed description of the preferred embodiments thereof which description should be considered in conjunction with the accompanying drawing in which:

FIG. 1 is a schematic, side elevation view of a portion of the preferred form of the apparatus of the invention;

FIG. 2 is an enlarged, side elevation view, partly in cross-section of the vacuum tube forming part of the apparatus shown in FIG. 1;

FIG. 3 is a circuit diagram of a preferred form of the electrical circuit for energizing the vacuum tube illustrated in the preceding figures; and

FIG. 4 is a fragmentary, schematic, side elevation view of an alternate form of a portion of the apparatus shown in FIG. 1.

The apparatus illustrated in FIG. 1 comprises a vacuum tube 10 having an anode 11, a target electrode 12 and a gas inlet tube or pipe 13. The inlet tube or pipe 13 is connected to a bottle or container 14, which contains a gas such as deuterium or tritium depending on the nature of the substance forming the surface of the target 12 as will be explained hereinafter. Valve 15 is included in series with the pipe 13 for controlling the entrance of the gas from the bottle 14 into the vacuum tube 10.

Since the yield of neutrons is proportional to the purity of the gas introduced into the tube 10, the gas in the container 14 preferably is of relatively high purity, i.e;, ninety percent or higher if high yields such as those described herein are desired, but a lower purity gas may, be employed if lower yields are acceptable.

The anode 11 is supported by a conductive rod 16 which is connected at one end to one terminal of the secondary winding 17 of a pulse transformer also having a primary winding 18. The opposite terminal of the secondary winding 17 may be connected to the tank 19 which contains an insulating oil 20. One terminal of the primary winding 18 is connected by a lead 21 which extends through an insulator 22 mounted through the wall of the tank 19 to a pulse voltage source hereinafter described. The other terminal of the primary winding 18 may be connected to the tank 19 which may, for example, be made of metal and may be grounded.

If desired, the secondary winding 17 may be formed by turns of the tube which supplies the gas from the container 14 to the tube 10, and the connection to the rod 16 may be omitted as illustrated in FIG. 4. In such alternate construction, the container 14 may be located externally of the tank 19, the tube 13 passing through the wall of the tank 19 and being grounded thereat and sealed thereto.

The vacuum tube may be continuously evacuated 3 through a pipe or line 23 which is connected to a conventional diffusion pump (not shown). The vacuum tube may also be connected by means of a pipe or line 24 to a vacuum gauge 25 diagrammatically illustrated in FIG. 1.

The vacuum tube 10 is illustrated in greater detail in FIG. 2 and comprises a cylinder 26 made of an insulating material, such as glass, which may be evacuted. In one embodiment of the invention, we employed a glass cylinder four inches in diameter and fifty centimeters long. Preferably, in order to improve the stability of operation, the cylinder 26 is coated on its inner wall with a thin, high resistance layer 27 of metal which prevents distortion of the electric field within the cylinder 26, such as by the non-uniform accumulation of static charges on the inner wall of the cylinder 26. The layer 27 may be provided by a conventional sputtering process in which the inner wall of the cylinder 26 is subjected to a direct current glow discharge under an impressed voltage of about 5,000 volts for a period of ten to twenty hours. The metals conventionally employed for such a layer, such as brass or stainless steel, may be used to form the layer 27.

A pair of metal cylinders 28 and 29, such as cylinders of a well known iron-nickel-cobalt alloy sold under the trademark Kovar alloy, are sealed to the ends of the cylinder 26 in a conventional manner and so as to provide a vacuum tight seal therewith and are in contact with the ends of the layer 27. Metal rings 30 and 31 are soldered, welded or otherwise secured to the ends of the cylinders 28 and 29.

The anode 11, which preferably is made of electropolished stainless steel but which may be made of other metals, is secured to the metal rod 16 in any conventional manner such as by soldering or welding. The rod 16 passes through a plate 32 to which the rod 16 is secured in a conventional manner, and the plate 32 is held against the ring 31 by means of bolts 33 extending through holes near the peripheries of the ring 31 and the plate 32, a gasket such as a rubber O-ring 34 being interposed between the ring 31 and the plate 32. The pipe 13 may pass through the plate 32 as illustrated and is secured thereto.

The target 12 comprises an exteriorly threaded metal disc 35, such as a disc of brass or stainless steel, secured to the end of a rod 44a, a thin sheet 36 of a metal such as platinum having on the outer surface thereof a target layer 37 and an interiorly threaded retaining ring Preferably the layer 37 is a layer, approximately 1.4 10- centimeters thick, of zirconium which has been deposited on the sheet 36 by vacuum deposition and in which about 30 curies of tritium gas is occluded. Such a sheet 36 with such a layer thereon is readily obtainable on special order from the Atomic Energy Commission, Oak Ridge, Tennessee. The type of metal used for the sheet 36 is not critical since it serves only as a mechanical support for the zirconium deposit and materials other than zirconium may be employed. However, it is essential that the layer contains one of the types of nuclei which when struck by the ions of the gas will produce neutrons of the desired energy. Thus, if deuterium gas is introduced by way of the pipe 13, the layer 37 contains tritons for producing high energy neutrons or contains deuterons for producing lower energy neutrons. On the other hand, if tritium gas in introduced into the tube by way of the pipe 13, the layer 37 contains deuterons and will produce high energy neutrons.

The yield of neutrons with the apparatus and methods of the invention is proportional to the number of re acting nuclei contained in the layer 37, and while the nuclei content indicated above provides high yields of the magnitude heretofore described, a lower nuclei content may be used if lower yields are acceptable.

A rotatable, threaded rod 44 extends through a thread ed opening in a plate 39 secured to a metal ring 40 such as by soldering or welding. A metal bellows 41 is secured to the metal plate 39 at one end and to a metal plate 42 at its opposite end, the plate 42 being adjustable in position by the rod 44.

A metal cylinder 43 having the pipes 23 and 24 extending therefrom is secured at its opposite end to a pair of metal rings 45 and 46 which are fastened respectively to the metal rings 40 and 30 by means of bolts 47 and 48 extending through holes adjacent the peripheries of said rings, rubber O-rings 49 and 50 being interposed between the rings as illustrated.

The assembly of parts shown in FIG. 2 and described above constitutes a vacuum tight assembly except for the openings for the inlet pipe 13 and the exhaust pipe 23. The dimensions of the parts and the materials used therefor are not critical, and various dimensions and materials may be employed without substantially affecting the performance of the apparatus.

The electrodes 11 and 12 preferably are energized by a high voltage, radar type modulator which produces rectangular voltage pulses of a duration adjustable from 1 to 14 microseconds, such as the modulator illustrated in FIG. 3. The circuit illustrated in FIG. 3 comprises a gas tube 51, such as a hydrogen thyratron, having a cathode 52, a control electrode 53 and an anode 54. The control electrode 53 is connected to the cathode 52 and to ground through a resistor 55 and is connected to a conventional trigger circuit 56 which supplies triggering pulses at the desired rate and with an amplitude sufficient to cause the gas tube 51 to conduct periodically or at spaced intervals. The anode 54 is connected to the positive terminal 57 of a high voltage power supply (not shown) through a choke 58 and a resistor 59. The junction point of the choke 58 and the resistor 59 is connected to the input of a conventional L-C delay or lumped line (it) having, for example, an impedance of 4.2 ohms. The line 60 is charged initially to the voltage at the terminal 57 and when the gas tube 51 conducts, the line 60 discharges through the primary winding 18. If the load across the secondary 17 is adjusted to the proper impedance value so that the primary 18 of the transformer presents a matching impedance to the line 60, a rectangular voltage pulse of a duration equal to twice the travel time of the voltage step along the line 60 will appear at the terminals of the secondary winding 17. The width of the voltage pulse at the terminals of the winding 17 may be varied by varying the number of elements in the line 60.

In one embodiment of the invention the turns ratio of the pulse transformer comprising the windings 17 and 18 was 22 to 1 and therefore a secondary load impedance of 2,000 ohms was required in order that the impedance seen by the line 60 at the primary winding 18 has a value of 4.2 ohms. With components of this value, it was found to be possible to produce an output voltage pulse at the terminals of the winding 17 which was substantially rectangular in shape and had a uniform peak amplitude of approximately 220 kilovolts.

The dynamic impedance of the discharge tube 10 during the voltage pulse is a function of time as well as of the pulse voltage. At the initiation of the applied pulse, before ionization has begun in the tube 10, the impedance of the tube 10 is extremely high. It is well known from the theory of modulators of the type illustrated in FIG. 3 that under these conditions an initial high voltage excursion in the pulse will occur with the impedance mismatch at the beginning of the voltage pulse. Such high voltage excursions produce instabilities in the discharge through the tube 10 and to insure that the waveform of the voltage pulse i substantially rectangular and smoothly reaches the desired level, the load presented to the secondary winding 17 of the pulse transformer, with the component values given above, should be nearly 2,000 ohms during the entire duration of the voltage pulse. In the apparatus illustrated in FIG. 3, this condition is achieved by con necting a resistor 61 having a resistance value close to, and preferably higher than, the desired impedance value across the secondary winding 17, and hence, in parallel with the electrodes 11 and 12 of the tube 10, a 2800 ohm resistor being found to be satisfactory, and by maintainingthe gas pressure within the tube at approximately x10 millimeters of mercury. When operated under these conditions, it has been found that no initial high voltage excursions, due to an impedance mismatch, arise to produce discharge instability.

Stability of the discharge is also improved by the use of the choke 58 illustrated in FIG. 3 which increases the time taken for the voltage pulse to reach its maximum amplitude. With components having the values indicated heretofore, it has been found that a choke having an inductance of 1 microhenry provides such improved stability.

Preferably the gas which is introduced into the tube 11) is introduced adjacent the anode 11 so as to assure that the gas is distributed evenly throughout the tube 10 and to assist in flushing of foreign gases which may be emitted from the walls of the tube 10 during the discharge. This means, however, that the gas supply and the control system which are electrically in contact. with the anode 11 will be raised to voltages above 150 kilovolts during the application of the voltage pulse. Accordingly, electrical discharges from such equipment and the anode end of the tube 10 may readily occur outside of the tube 10 if the apparatus is operated in air. For this reason, the components subjected to high voltage are immersed in an insulating oil 20 within the tank 19 as illustrated in FIG. 1.

The voltage between the electrodes 11 and 12 and the pressure within the tube 19 are important factors in obtaining high neutron yields and stable operation. When the voltage is below 100 kilovolts, the neutron yield is insignificant, but as the voltage is increased above 100 kilovolts, the neutron yield increases rapidly. Because of the practical difficulties in using higher voltages, such as arcing, generating the voltages, insulation problems, etc., it is preferable to operate at Voltages up to 200 kilovolts. Operation at higher voltages with thicker targets and better insulation will produce higher yields and is within the scope of the invention.

The voltage selected is affected also by the gas pressure in the tube 10 which in turn affects the neutron yield. Thus, a graph of neutron yield versus applied voltage with varying gas pressures shows that with higher pressures, the curve of neutron yield versus voltage rises more steeply than such curve under lower pressure conditions. Thus, with a pressure of microns and a given voltage, a much greater neutron yield will be obtained than with a 10 micron pressure and the same voltage. On the other hand, the breakdown voltage of the gas within the tube 10, that is, the voltage at which the current between the electrodes 11 and 12 increases rapidly with substantially no further increase in the applied voltage, is lower with higher pressures than with lower pressures. Since the apparatus is unstable when a voltage equal to or greater than the breakdown voltage is employed, the voltage is Selected so as to provide suflicient ion energy to operate in the region of maximum neutron yield as determined by voltage considerations alone, i.e. 150 to 200 kilovolts, and the pressure is selected so as to provide about the maxiinum neutron yield for the selected voltage without exceeding the pressure at which breakdown occurs for the selected voltage. Thus, for a voltage of 150 to 200 kilovolts, a maximum neutron yield with stable operation is obtained with a pressure of about 20 microns, which, it will be noted, is not a high vacuum of the type employed with prior art apparatus or conventional vacuum tubes. The preferred and useful range of voltages extends from about 125 to 220 kilovolts with corresponding pressures 6 of about 30 microns for kilovolts and 15 microns for 220 kilovolts.

During operation of the apparatus, the tube 10 is continuously evacuated by means of the pump connected to the pipe or line 23 and the inflow of the gas contained in the bottle 14 is controlled by means of the valve or variable leak 15. By adjusting the rate of pumping and the rate at which the gas enters the tube 10 through the line 13 the pressure within the tube 10 can be adjusted to a level of about 20 microns and can be held within 1 micron of this level for over an hour. The high voltage pulses applied to the electrodes 11 and 12 cause high speed nuclei and molecule-ions to strike the tritiated surface 37 of the cathode 12. If the voltage between the electrodes 11 and 12 is about 100 kilovolts or greater, the nuclei and molecule-ions have sufiicient energy to cause a neutron producing reaction at the surface 37. Thus, if the bottle 14 contains deuterium, high speed deuterons and deuterium molecule-ions strike the tritiated surface 37 producing high energy neutrons. Similarly if the bottle 14 contains tritium, high speed tritons and tritium molecule-ions strike the deuterated surface 37 again producing high energy neutrons at the surface 3'7.

In one typical embodiment of the invention, the voltage pulse applied to the tube 16 had a voltage amplitude of kilovolts. Under these conditions a current of 30 amperes passed through the tube 10 and a current of 75 amperes passed through the parallel resistance 61. About 6 amperes of the current of the tube 10 was composed of deuterons which struck the target electrode 12 and induced the neutron producing reaction. Yields as high as 1.0x 10 neutrons per pulse have been obtained, and it was found that operating voltages and currents were not critical except to the extent described above and could be varied to vary the neutron yield.

The high energy neutrons emerge isotropically from the layer 37, and due to the presence of the oil 20 (FIG. 1), those neutrons emerging other than upwardly from the layer 37 as viewed in FIG. 1 are highly attenuated. Accordingly, an object to be irradiated preferably is located in the path of such neutrons above the upper surface of the oil 20, but it will be understood that if the object can be placed in the oil 20 adjacent the wall of the tube 10 such an object would also be irradiated by neutrons emerging from the layer 37.

As pointed out above, the apparatus of the invention also constitutes a copious and sustained source of ions and may be used as such with improved results as compared to known types of ion sources. When used as such a source the neutron producing layer 37 and the cathode 12 and its supporting structure may be omitted, the rings 39, 45 and 46 and the cylinders 28 and 43 acting as a conventional apertured accelerating electrode to permit the ions to pass therethrough to the point at which the ions are to be utilized, and if desired, other modifications which will be readily apparent to those skilled in the art may be made to adapt the apparatus to a specific application as an ion source.

Having thus described our invention with particular reference to the preferred form thereof, it will be obvious to those skilled in the art to which the invention pertains, after understanding our invention, that various changes and modifications may be made therein without departing from the spirit and scope of our invention, as defined by the claims appended thereto.

What is claimed as new and desired to be secured by Letters Patent is.

l. Neutron generating apparatus comprising a vacuum tight tube of insulating material having a gas inlet and an anode at one portion thereof, means connected to said gas inlet for supplying a gas selected from the group consisting of deuterium gas and tritium gas to said tube, a cathode mounted at another portion of said tube and having a target layer facing said anode, said layer comprising nuclei selected from the group consisting of deuterons and tritons but different from the nuclei of said gas, said tube having a gas outlet at said other portion thereof, a coating of conductive material on the interior wall of said tube intermediate said cathode and said anode, a resistor connected between said anode and said cathode, and a high voltage pulse source having a positive terminal connected to said anode and a negative terminal connected to said cathode.

2. Neutron generating apparatus comprising means containing an insulating fluid, a vacuum tight tube of insulating material mounted with its lower portion immersed in said fluid, said tube having a gas inlet and an anode at the lower end thereof, means connected to said gas inlet for supplying a gas selected from the group consisting of deuterium gas and tritium gas to said tube, a pulse transformer immersed in said fluid and having primary and secondary windings, means connecting one portion of said secondary winding to said anode and another portion of said secondary winding to one portion of said primary winding, a resistor connected between said portions of said secondary winding, a cathode mounted at the upper end of said tube and having a target layer facing said anode, said layer comprising nuclei selected from the group consisting of deuterons and tritons but different from the nuclei of said gas, means connecting said other portion of said secondary winding to said cathode, said tube having a gas outlet in said upper end thereof, a coating of conductive material on the interior wall of said tube intermediate said cathode and said anode, and a high voltage pulse source connected to said primary winding, said primary winding and said secondary winding being polarized relative to each other so as to apply positive potential to said anode and negative potential to said cathode.

3. Neutron generating apparatus comprising means containing an insulating fluid, a vacuum tight tube of insulating material mounted with its lower portion immersed in said fluid, said tube having a gas inlet and an anode at the lower end thereof, means connected to said gas inlet for supplying a gas selected from the group consisting of deuterium gas and tritium gas to said tube, a pulse transformer immersed in said fluid and having rimary and secondary windings, means connecting one portion of said secondary winding to said anode and another portion of said secondary winding to one portion of said primary winding, a resistor connected between said portions of said secondary winding and having an impedance substantialiy equal to the impedance of said tube during operation, a cathode mounted at the upper end of said tube and having a target layer facing said anode, said layer comprising nuclei selected from the group consisting of deuterons and tritons but different from the nuclei of said gas, means connecting said other portion of said secondary winding to said cathode, said tube having a gas outlet in said upper end thereof, a coating of high resistance, conductive material on the interior wall of said tube intermediate and electrically connected to said cathode and said anode, a gas tube having control, anode and cathode electrodes, means connecting said cathode electrode to said first-mentioned cathode, a choke having one end thereof connected to said anode electrode, means including a resistor for connecting the other end of said choke to an electrical energy source, and a delay line connected between said other end of said choke and another portion of said primary winding.

4. Neutron generating apparatus comprising means containing an insulating fluid, a vacuum tight tube of insulating material mounted with its lower portion immersed in said fluid, said tube having a gas inlet and an anode at the lower end thereof, a container or tritium gas immersed in said fluid and connected to said gas inlet for supplying gas to said tube, a pulse transformer immersed in said fluid and having primary and secondary windings, means connecting one end of said secondary winding to said anode and the other end of said secondary winding to one end of said primary winding, a resistor connected between the end of said secondary winding and having an impedance substantially equal to the impedance of said tube during operation, a cathode mounted at the upper end of said tube and having a target layer facing said anode, said layer having deuterium gas occluded therein, means connecting said other end of said secondary winding to said cathode, said tube having a gas outlet in said upper end thereof, a coating of conductive material on the interior wall of said tube intermediate and electrically connected to said cathode and said anode, a gas tube having control, anode and cathode electrodes, means connecting said cathode electrode to said firstmentioned cathode, a choke having one end thereof connected to said anode electrode, means including a resistor for connecting the other end of said choke to an electrical energy source, and a delay line connected between said other end of said choke and the other end of said primary winding.

5. Neutron generating apparatus comprising means containing an insulating fluid, a vacuum tight tube of insulating material mounted with its lower portion immersed in said fluid, said tube having a gas inlet and an anode at the lower end thereof, a container of deuterium gas immersed in said fluid and connected to said gas inlet for supplying gas to said tube, a pulse transformer immersed in said fluid and having primary and secondary windings, means connecting one end of said secondary winding to said anode and the other of said secondary winding to one end of said primary winding, a resistor connected between the ends of said secondary winding and having an impedance substantially equal to the impedance of said tube during operation, a cathode mounted at the upper end of said tube and having a target layer facing said anode, said layer having tritium gas occluded therein, means connecting said other end of said secondary Winding to said cathode, said tube having a gas outlet in said upper end thereof, a coating of conductive material on the interior wall of said tube intermediate and electrically connected to said cathode and said anode, a gas tube having control, anode and cathode electrodes, means connecting said cathode electrode to said first-mentioned cathode, a choke having one end thereof connected to said anode electrode, means including a resistor for connecting the other end of said choke to an electrical energy source, and a delay line connected between said other end of said choke and the other end of said primary winding.

6. Neutron generating apparatus comprising a vacuum tight tube of insulating material having a gas inlet and an anode at one portion thereof, a cathode mounted at another portion of said tube, said tube having a gas outlet at said other portion thereof, a high voltage pulse source including an output transformer having primary and secondary windings, said secondary winding being formed by hollow turns of conductive material, means mechanically connecting one end of saidusecondary winding to said gas inlet and electrically connecting said end to said anode, means electrically connecting the other end of said secondary winding to said cathode and means connected to said other end of said secondary winding for supplying a gas selected from the group consisting of deuterium gas and tritium gas through said secondary winding and to said tube, said cathode having a target layer facing said anode and said layer comprising nuclei selected from the group consisting of deuterons and tritons but different from the nuclei of said gas.

7. Neutron generating apparatus comprising means containing an insulating fluid, a vacuum tight tube of insulating material mounted with its lower portion immersed in said fluid, said tube having a gas inlet and an anode at the lower end thereof, a pulse transformer immersed in said fluid and having primary and secondary windings, said secondary winding being formed by hollow turns of conductive material, means mechanically connecting one end of said secondary winding to said gas inlet and electrically connecting said end to said anode, means connected to the other end of said secondary Winding for supplying a gas selected from the group consisting of deuterium gas and tritium gas through said sec ondary winding and to said tube, a resistor connected between said ends of said secondary winding, a cathode mounted at the upper end of said tube and having a target layer facing said anode, said layer comprising nuclei selected from the group consisting of deuterons and tritons but different from the nuclei of said gas, means electrically connecting said other end of said secondary winding to said cathode, said tube having a gas outlet in said upper end thereof, a coating of conductive material on the interior wall of said tube intermediate said cathode and said anode, and a high voltage pulse source connected to said primary winding.

References Cited by the Examiner UNITED STATES PATENTS 2,689,918 9/54 Yournans 31361 2,926,271 2/60 Brinkerhofif 250-84.5 2,933,611 4/60 Foster 250-845 2,9 67,943 1/61 Gow 250-84.5 2,994,777 8/61 Tittle 25084.5

RALPH G. NELSON, Primary Examiner. 

1. NEUTRON GENERATING APPARATUS COMPRISING A VACUUM TIGHT TUBE OF INSULATING MATERIAL HAVING A GAS INLET AND AN ANODE AT ONE PORTION THEREOF, MEANS CONNECTED TO SAID GAS INLET FOR SUPPLYING A GAS SELECTED FROM THE GROUP CONSISTING OF DEUTERIUM GAS AND TRITIUM GAS TO SAID TUBE, A CATHODE MOUNTED AT ANOTHER PORTION OF SAID TUBE AND HAVING A TARGET LAYER FACING SAID ANODE, SAID LAYER COMPRISING NUCLEI SELECTED FROM THE GROUP CONSISTING OF DEUTERONS AND TRITRONS BUT DIFFERENT FROM THE NUCLEI OF SAID GAS, SAID TUBE HAVING A GAS OUTLET AT SAID OTHER PORTION THEREOF, A COATING OF CONDUCTIVE MATERIAL ON THE INTERIOR WALL OF SAID TUBE INTERMEDIATE SAIC CATHODE AND SAID ANODE, A RESISTOR CONNECTED BETWEEN SAID ANODE AND SAID CATHODE, AND A HIGH VOLTAGE PULSE SOURCE HAVING A POSITIVE TERMINAL CONNECTED TO SAID ANODE AND A NEGATIVE TERMINAL CONNECTED TO SAID CATHODE. 